Our long-term research objective is to understand the mechanisms by which the body segments of Drosophila become morphologically differentiated from one another. A central role in this process is played by the genes of the bithorax complex (BX-C), a cluster of three large genes that controls the identities of segments in the posterior thorax, abdomen and genitalia. A major objective of the research proposed is to identify sites within the BX-C that are important for its spatial regulation. Our approach will be to map sites within the chromatin of the BX-C that are hypersensitive to cleavage by DNase I and methidiumpropyl-EDTA iron(II). Analysis of other genes indicates that such sites almost always identify important cis-acting sequences. Assessment of which hypersensitive sites are involved in spatial regulation will be made by determining which are segment- or tissue-specific and which require known BX-C regulatory gene products for their establishment or maintenance. A second specific aim of our work on the BX-C is to determine whether the regulatory regions of adjacent genes in the BX-C overlap. Another major goal of the proposed research is to define features targeting the protein encoded by fushi tarazu (ftz), a key regulator of the BX-C, for rapid degradation. Regions determining instability will be localized by analysis of truncated ftz-beta-galactosidase fusion proteins, and the importance of specific amino acids within the regions identified will be assessed by in vitro mutagenesis. To identify the proteolytic system responsible for rapid ftz degradation, mutations causing persistence of ftz stripes during embryogenesis will be selected. In other work related ftz, experiments are proposed to test the "combinatorial" model of pair-rule gene action and to determine why segmentation defects occur in the ftzUal mutants, which stabilize the ftz protein. A third major goal is the characterization of the homeotic gene spineless- aristapedia (ssa). A standard molecular analysis is proposed. Using antibodies, expression of ssa proteins will be examined in appropriate genotypes to determine whether ssa participates in cross-regulatory interactions with other homeotic genes or shares trans-regulators with them. To test whether ssa is the primary determinant of distal antennal identity, the effects of ectopic expression of ssa proteins in the distal legs will determined. The health significance of the proposed research is that it may lead to a better understanding of how homeotic gene complexes are regulated in human embryogenesis and how, therefore, certain congenital abnormalities arise.